Immunoassay devices and procedures currently exist for detecting the presence of an analyte in a sample of biological fluid. Typically, immunochemical reactions involving antigen/antibody reactions take place on dry porous carriers such as cellular membranes through which the sample to be analyzed flows by capillary action. The presence of an analyte in the sample can be detected either visually or by using reflectance or fluorescence based detection systems and instruments. Oftentimes, the label is an enzyme label or a particulate direct label, for instance a gold sol label.
Typical immunochromatographic devices of this nature are described in the following U.S. Pat. Nos. 4,094,647; 4,235,601; 4,361,537; 4,703,017, 4,774,192; 4,839,297; 4,861,711; 4,885,240; 4,960,691; 5,075,078; 5,079,142; 5,110,724; 5,120,643; 5,135,716; 5,468,648; 5,591,645; 5,607,863; 5,622,871; 5,648,274; 5,656,503; 5,846,838; 5,869,345; 5,877,028; 5,998,220; 6,017,767; 6,168,956; 6,171,870; 6,187,598; 6,214,629B1; 6,228,660; 6,528,321; and 6,534,320.
U.S. Pat. No. 5,290,678 describes an analytical test kit incorporating a dry chemistry membrane comprising antibody pairs to multiple analytes observed during cardiovascular events. In operation of the device, multiple transfer steps are required before analysis and further this device is only designed for receiving samples of serum or plasma and as such is not suitable for analyses using whole blood.
U.S. Pat. No. 5,559,041 discloses an immunoassay device with a membrane array comprising an overlapping arrangement of a reservoir pad, numerous membrane filters and a wicking membrane all with an equal range of pore sizes. In the use of this device, rapid and high sensitivity analysis of analyte concentrations cannot be achieved with small sample sizes.
PCT/IB2003/005088 describes a membrane array and analytical device designed for the sensitive detection of analytes from a sample of fluid as small as a drop. The membrane array comprises a two membrane system including a first separation membrane and an analytical capture membrane. However, rapid and high sensitivity detection of analytes using whole blood is not achievable in all circumstances and membrane array constructions with small sample volumes without background interference caused by hemolysis (the liberation of hemoglobin from the red blood cell).
While the aforementioned devices are generally useful for detecting analytes in a sample, it is desirable to provide an analytical device which has greater sensitivity using smaller sample volumes and at the same time provides a rapid test result. Thus, there is a need to develop an analytical device that is designed to obviate some of the deficiencies of the prior art devices.